Advanced Turbocharged, Direct Injected Gasoline Engines Poised to Take on Diesels in US and in Europe for Reduced Fuel Consumption and Emissions
A confluence of technology developments, future emissions regulations and economic conditions will not only allow advanced light-duty spark-ignited gasoline engines to keep diesels at bay in the US market, but may also allow the gasoline units to push into the diesel-dominated medium-duty commercial truck and off-highway segments in the US, according to several presentations at the US Department of Energy’s 2009 Directions in Engine-Efficiency and Emissions Research (DEER) conference last week.
Additionally, suggested one of the speakers, advanced SIDI (spark-ignited, direct-injection) engines can take light-duty market share back from diesels in Europe based on the same trends.
SULEV/Tier 2 Bin 2 is the target. Tom Cackette, Chief Deputy Executive Office of the California Air Resources Board, spent the bulk of his talk during the opening panel discussing the response to climate change, which he called “the defining environmental challenge of this century.” However, prior to the remarks on climate change and the regulatory response, he spent a few minutes discussing the efforts on urban pollution—e.g., smog and particulates.
What more is need to end urban pollution, something we’ve been spending over 30 years working on? First of all, future passenger vehicles have to stay as clean as the best vehicles out there today. Some of the best passenger vehicles today, the ones called PZEVs, are pretty close to zero emissions.—Tom Cackette
Under California’s vehicle emissions ratings, PZEVs (Partial Zero Emission Vehicles) meet SULEV (Super Ultra Low Emission Vehicle) tailpipe emission standards and also have zero evaporative emissions. The SULEV standard, established under the current LEV II regulation, is equivalent to the Federal Tier 2 Bin 2 standard.
|Comparison of Emission Standards (g/mi)|
|Current 50-state baseline||Projected future baseline|
|US T2B5||CA LEV||US T2B2||CA SULEV|
California’s current LEV II emission standards run through 2010. Cackette was in effect suggesting that the future tailpipe emissions baseline (LEV III) for light duty passenger vehicles—both diesel and gasoline—was likely to be or to approximate CA SULEV/US Tier 2 Bin 2.
This was reinforced during a subsequent presentation by Robert Czarnowski, of Borg Warner, on that company’s new control strategy for a dual loop EGR system to meet projected future emissions standards.
Bin 5 is no longer the target, it’s SULEV. That’s difficult, but doable. Bin 5 engine out is what we’ll need, and then to get it down to Bin 2.—Robert Czarnowski
Tim Johnson, from Corning, in his review of diesel emission control technology at the conference, started as is his practice by a quick regulatory review.
We heard a little bit from Tom Cackette yesterday about LEV III...I think this is the beginning of another round of criteria pollutant reductions, so we might not be done yet if history repeats itself.—Tim Johnson
The prospects of additional development cost—plus the resulting higher price of the final vehicle—to meet more stringent regulations is giving automakers pause, according to Paul Whitaker from AVL, as he presented their solution for a turbocharged spark ignited direct injection engine development for the US.
Customers are now beginning to demand more fuel efficient vehicles, and recent legislation is mandating 40% improvement in ...fuel economy between now and 2016. So it’s clear that significant changes need to be made to the vehicle fleet.
...Given the financial challenges facing the auto industry, the powertrain solutions need to meet customer approval and need to be manufacturable...so the manufacturing can be profitable and also very competitive. Many improvements in fleet fuel economy in Europe have been achieved through increased diesel market share, with the diesel market share in Europe now above 50%.
But if we look at the challenge of bringing current European diesel applications to the US, we can see that there is a significant challenge in moving from Euro 5 to Tier 2 Bin 5 or LEV II, which is really the point of entry into the US. We’re talking about a 76% reduction in NOx which in itself has had a significant increase in cost to diesel application in North America...For the future, we really need to be considering SULEV or Bin2. These are likely to drive further increases in cost, and potentially further reductions in fuel efficiency.
So there are going to be some big challenges, and I think we’ll see...that a lot of the plans for diesel introductions for light duty applications have been cancelled...I don’t think we expect to see a large market share of light duty diesel in the short term.—Paul Whitaker
Advances in SIDI. There were a variety of approaches to advancing the gasoline platform via a turbocharged, spark-injected direct-injection (SIDI) approach presented at the DEER conference.
John Kirwan from Delphi presented a 3-cylinder turbocharged SIDI concept, “a high value solution for meeting Euro 6 in smaller passenger cars”.
We see dramatic downsizing and boosting [as] something that’s going to for gasoline engines especially. We also expect a lot of hybrids and electrification.—John Kirwan
The basic approach of the downsized 3-cylinder gasoline direct injection (GDI) engine is to reduce engine displacement and decrease engine speed (downsizing and downspeeding) to increase engine load for improved specific fuel consumption. To be able effectively to implement downsizing and downspeeding, good low-end torque is essential. The challenge with smaller engine, Kirwan said, is to get good boosting at low engine speeds.
Direct injection, combined with cam phasing, improves volumetric efficiency by enabling very good scavenging at full loads to reduce the residual gas fraction in the cylinder.
Without direct injection, if you try to do scavenging of fresh air into the cylinder, what happens is you mix the fuel with the air and so you are exhausting a lot of hydrocarbons into the exhaust. With direct injection, you can push the air through the cylinder, you have valve overlap. With the valve overlap, you are forcing fresh air up into the exhaust, but since you inject the fuel later you don’t have any hydrocarbons from the fuel going into the exhaust. That’s one of the reasons you get better scavenging, better scavenging of course gives you more fresh air that you can burn with the fuel.—John Kirwan
Direct injection also reduces knock propensity, and supports improved combustion phasing.
Kirwan cited a 2008 paper by GM engineers presented at the Vienna Motor Symposium that found fuel economy improvement of 9-15% for homogeneous GDI systems, and improvements of up to 15-21% for stratified systems. (Königstein (lecturer), Larsson, Grebe, Wu. “Differentiated Analysis of Downsizing Concepts”).
Kirwan noted that with three cylinders at full load, you can do better scavenging, better engine breathing than with four. Three cylinders also support reduced fuel consumption and emissions. Kirwan also noted that three-cylinder engines increase NVH. However, he said, based on Delphi’s analysis, for engine displacement of less than 1.5 liters, the three cylinder engine is the preferred configuration.
Moving up into large light-duty or medium-duty sectors, Rod Beazley from Ricardo highlighted a 3.2-liter V-6 Ethanol-Boosted Direct Injection (EBDI) prototype, which is capable of operating on gasoline or up to 100%. (Earlier post.)
The EBDI project is designed to increase the thermal efficiency of a spark-ignited engine, and combines the following technologies:
- Reduced engine displacement
- Increased cylinder pressure envelope
- Cooled exhaust gas recirculation (EGR) under boosted conditions
- Advanced boosting concepts
- Variable valve timing and lift under throttled conditions
- Direct injection fueling
- Optimized control algorithms for flex-fuel capability
The engine under development is targeted to achieve 35 bar BMEP on E85 (30 bar on E0), delivering the performance of a 6.6-liter V8 diesel in a full size pickup truck without any deterioration in vehicle performance or driveability, including towing capability. That level of performance equates to a 450 hp (336 kW) 900 N·m (664 lb-ft) engine on E85.
To maximize efficiency and minimize tailpipe emissions, the concept utilizes stoichiometric combustion at full load with exhaust temperature controlled via the use of EGR as a diluent fluid. This combustion concept allows the use of a three-way catalyst (TWC) as the sole required after-treatment device.
Beazley said that without a doubt, this is the largest project Ricardo has undertaken in the US.
Why we developed the EBDI concept...about two years ago, many of you will remember, in the light duty field, there were probably between 40 to 45 diesel programs being developed in the US for light duty applications. From a spark-ignited engineer’s perspective, this became a bit of a threat, you know, to our livelihood...Fortunately or unfortunately depending upon your view, with fuel prices rocketing up last year to $5 per gallon for diesel...most of the diesel programs have now gone by the wayside, people are now looking at more and more advanced spark ignited [engines] in passenger cars, a lot of downsizing and boosting. Similarly we see the trend in Europe, where it was predominantly between 55 to 60 percent diesel...with the advanced spark ignited in Europe, that trend is now gasoline engines at 52 to 53 percent.—Rod Beazley
|The Ford/AVL dual fuel E85-gasoline strategy. Click to enlarge.|
AVL is taking a different approach to advancing spark-ignited technology, working with the ethanol boosting concept being explored by Ford, also in collaboration with Ethanol Boosting Systems (a spin-off from MIT) (earlier post)—the use of a separate E85 direct injection system combined with gasoline port injection to make the engine more efficient in its use of gasoline, and to optimize the benefit of the limited quantity of E85 available.
The E85 injection provides significant octane benefit due to the high latent heat of vaporization and high octane rating. This enables knock-free operation at a high compression ratio and high BMEP with very high thermal efficiency.
To summarize, future fuel economy improvements will come from a variety of technologies. I’m not proposing here that turbo direct injection in the only technology for fuel economy improvement for the US...but I think that it is probably fair to assume that gasoline engines will be the dominant US powertrain for the foreseeable future.
Turbocharged direct injection certainly seems to be one of the most promising advanced gasoline technologies...it offers double digit fuel economy benefits at lower a cost lower cost than diesel or hybrid; it can meet future emissions standards with an inexpensive three-way catalyst; it can be applied across an entire engine portfolio; and it provides benefits when operating on E85 in flex-fuel applications.—Paul Whitaker